Abstract : The purpose of this chapter published in a book dedicated to the use of geomedia in secondary education is to emphasize the role of geomedia for designing a playful learning situation. We describe Clim@ction, a French-Canadian online role-play game about land use management. Clim@ction involves the students in collaboration and competition for a project designed for implementing green energies in a local territory. The learning situation offers secondary students a complex and non-deterministic problem. Therefore, it is expected that they develop a broad and realistic view regarding the issue of sustainable development. In this chapter, we describe the background of our project related to personal epistemology and to Game-Based Learning. We also underline the use of geomedia for designing the game, and we present the results of an experimentation carried out by teachers and researchers in France and Québec.